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simulation, the testing and a summary of the performance of the deck. .... written in the software PYTHON to output the results and to plot strength–strain curves.
XVIII EDICIÓN Curso Máster de Estudios Mayores de la Construcción

C E M C O 14.15

Innovación, Tecnología y Sostenibilidad en la Construcción CEMCO 2014-15

TRABAJO FIN DE CEMCO

Autor Marco F. Gallegos C. (Ecuador)

Directores del Trabajo M. Dolores G. Pulido Khanh Nguyen G.

Madrid, diciembre de 2015

Instituto de Ciencias de la Construcción Eduardo Torroja, IETcc-CSIC

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THEORETICAL AND EXPERIMENTAL PERFORMANCE ANALYSIS OF A CELLULAR GFRP VEHICULAR BRIDGE DECK EVALUACIÓN TEÓRICA Y EXPERIMENTAL DEL COMPORTAMIENTO DE UN TABLERO GFRP CELULAR PARA PUENTE VEHICULAR Author:

Marco F. Gallegos C., [email protected]

Tutors:

M. Dolores G. Pulido, [email protected] Khanh Nguyen G., [email protected]

Abstract This report describes the research carried out at the Eduardo Torroja Institute for Construction Science (IETcc) - Spanish National Research Council (CSIC) to examine the behavior of glass fiber reinforced polymer (GFRP) bridge deck system under traffic loading. The main objective of the investigation was to study the local and global performance of the pultruded GFRP deck by both numerical models and experimental tests always in linear elastic conditions. Tests were performed on a specimen of a portion of deck system with 1,40 m of length, made from adhesively bonded cellular profiles, which was rigidly supported at its base. Static loads were applied via steel plate and elastomeric pad to various positions at the deck top face in order to simulate the passage of truck wheel. Models of this isolated specimen and single-span specimens – previously tested at IETcc in 2012 – were analyzed in this investigation using the standard FE software ABAQUS1, which used finite elements for modeling the deck including material and geometry anisotropies. The Finite Element results are comparable to those experimentally obtained, so the FEA developed in this work can reliably represent the structural response for these complex structures. Keywords: GFRP bridge deck, glass fiber, finite element analysis (FEA), mechanical testing.

Resumen Este trabajo describe la investigación realizada en el Instituto de Ciencias de la Construcción Eduardo Torroja (IETcc) – Consejo Superior de Investigaciones Científicas (CSIC), para examinar el comportamiento de un sistema de tablero para puente, elaborado de polímero reforzado con fibra de vidrio (GFRP), bajo cargas de tráfico. El objetivo principal de la investigación fue estudiar el desempeño local y global del tablero de GFRP pultrusionado mediante modelos numéricos y ensayos experimentales, siempre en el rango elástico lineal. Los ensayos se realizaron a un espécimen de una rebanada del sistema de tablero de 1,40 m de longitud, fabricada por unión adhesiva entre perfiles celulares, el cuál fue apoyado rígidamente en su base. Las cargas estáticas fueron aplicadas a través de una placa de acero y un cojín elastomérico para varias posiciones en la cara superior del tablero para simular el paso de una rueda de camión. Los modelos de éste espécimen aislado y especímenes de módulos enteros bi apoyados – previamente ensayados en el IETcc en 2012 – fueron analizados en ésta investigación usando el software estándar de FE ABAQUS, en el cuál se utilizó elementos finitos para la modelación del tablero incluyendo las anisotropías del material y la geometría. Los resultados de Elementos Finitos son comparables a aquellos obtenidos experimentalmente, por lo que el FEA desarrollado en este trabajo puede representar de forma fiable la respuesta estructural de estas estructuras complejas. Palabras clave: tablero de puente GFRP, fibra de vidrio, análisis por elementos finitos (FEA), ensayos mecánicos.

1

SIMULIA, Abaqus/CAE, v6.13, Dassalt Systemes SIMULIA Corp., 2013.

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1.

Introduction

1.1. Basic concepts Composite elements are obtained with a combination of two or more materials, each of which largely retains its own physical identity, to form a new material with enhanced properties, such as, concrete, wood, etc. The most common composites are those made with strong fibers held together in a matrix (resin). Fiber reinforced polymers (FRP) is one of this emerging composites. FRP have attracted the interest of many researchers in the field of civil engineering since the 1980s due to their high strength and low specific weight compared to the classical construction materials like concrete and steel. Although there are many types of FRP materials available, glass fiber reinforced polymers (GFRP) is preferred in practice where glass fiber exhibit the typical glass properties of hardness, corrosion resistance and inertness. Furthermore, they are flexible, lightweight and inexpensive. A cost-competitive method of producing high-quality constant-cross-section GFRP profile shapes for structural engineering use, named pultrusion, was developed during the 1950s in the United States. Pultrusion is an automated and continuous process – shown in Figure 1 –, which produces GFRP parts for structural engineering based on dry fibers impregnated with a low-viscosity liquid thermosetting polymer resin. After, they are guided into a heated chrome-plated steel die, where both are cured to form the desired GFRP part. Finally, the GFRP is cured as the material is pulled through the die by a pulling apparatus. Hence, it is named pultrusion (Bank, 2006).

Figure 1. A pultrusion line or a pultrusion machine is used to produce the pultruded GFRP profile shape. Source: http://www.nuplex.com/composites/processes/pultrusion

1.2. GFRP bridge decks In the field of bridge engineering, the concrete is likely to be the most common deck material because it is efficient and durable. However, some concrete bridge decks have suffered corrosion because of the increasing use of de-icing salts. In addition, the rapid growth in volume and weight of heavy goods vehicles has led to serious problems. Thus, many older bridges no longer meet current design standards. There is, therefore, a need for methods of replacing bridge decks to deal with structural deterioration and increase load capacity without extensive and expensive bridge works. Moreover, GFRP profile shapes have seen increased application since the mid-1970s. Both the light weight of the GFRP components and their noncorrosive properties serve to make them attractive to be used as bridge decking panels or superstructure members. In the 1990s, a significant effort was undertaken by a number of FRP manufacturers to develop a GFRP bridge deck system that could be used on conventional steel or concrete girders. The GFRP material properties of high strength and corrosion resistance could be the solution. Besides the potential for long-term durability of a GFRP bridge deck, the composite material could replace deteriorated reinforced concrete decks. Due to the significant decrease in dead weight of the structure, the live-load capacity for the re-decked structure can be increased. Hence, it may be beneficial, especially on bridges with load postings. Currently, most commercial bridge decks are made of GFRP because of their cost-effectiveness.

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GFRP bridge decks are fabricated in the form of thin walled structures with empty space inside by the pultrusion process. The walls of GFRP decks are continuous in the direction of the pultrusion which is called the longitudinal direction. On the other direction, called the transverse direction, those thin walls are connected to form a closed section. The shape of the cross section can be rectangular. Individual cellular profiles are bonded together to form a bridge deck. Because of the pultrusion process, the behavior of GFRP bridge decks is orthotropic. In addition, there is a strong nonlinearity on the transverse direction, which depends on the type of cross section. The nonlinearity is strongest in the rectangular section because of its low shear stiffness. However, simple rectangular sections are still preferred because they are easy to produce by the pultrusion process.

1.3. GFRP properties and design considerations The perceived lack of standard material specifications and test methods for GFRP composite materials, often given as a reason for not using GFRP products, is no longer a convincing reason for not specifying GFRP composites to be used in structural engineering. The characteristic properties of GFRP composite materials are usually obtained by experimental testings. In some situations, properties at higher levels are predicted from the experimentally determined properties at lower levels, using theoretical models. Many properties of FRP composite can be projected from the properties of the fiber and polymer resin system (known as the matrix in mechanics’ terminology). This fiber-level analysis is known as micromechanics. Both physical and mechanical properties can be predicted using micromechanics models. For structural engineering purposes, only simple micromechanics models, based on the rule of mixtures, are commonly used. In homogeneous isotropic materials such as steel, the material strength and stiffnesses do not depend on the section location, and the load-carrying capacity is determined relatively easily. However, in FRP members, the stiffness and strength properties are location dependent within the cross section on the fiber, lamina, and laminate levels due to the inhomogeneity and anisotropy of the material. The mechanical and physical properties of FRP materials used in these pultruded profiles are obtained from tests on coupons cut from the sections (i.e., on the laminate level) or from tests on panels that are produced by pultrusion with nominally identical properties. In certain situations, it is preferred to use full-section tests on individual profiles or on subassemblies of profiles to develop fullsection properties or capacities for use in design. Although theoretical methods are available to predict these properties from coupon data, this requires that the designer states a number of simplifying assumptions related to the profile’s geometry, homogeneity, and anisotropy. Full-section testing is a way to obtain an effective property for a profile that can be used in a stress-resultant theory. In the last four decades the finite element method (FEM) has become the most widely used numerical procedure for the approximate numerical solution of a system of differential equations and is therefore widely used in the analysis of structures with composite materials. Deck response under concentrated tire loading is influenced by two levels of statical indeterminacy in the bridge. One is the local indeterminacy of the cellular FRP frame. The other is the bridge’s global indeterminacy. A single span simply supported bridge is globally indeterminate due to the multiple beam supports at each end. Now, the stiffness profile of an indeterminate structure dictates the stress resultants developed in the structure under any given load. Thus, the stiffness profile representation is important if the internal stresses (and so strains) are to be reliably predicted. This is especially true for FRP deck bridges. FRPs are linear to fail, so the need to establish accurately the material stress capacity (for failure) has been taken up in resisting applied load is crucial. (Sebastian WM., 2012)

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1.4. Review of literature In recent years, many studies have been developed to show the in-service performance of several pultruded bridge decks. (Zhou, 2005) conducted Laboratory and field tests to evaluate the in-service performance according to AASHTO regulations of a traffic bridge deck composed from adhesively bonded pultruded plates and square tubes. (Park K., 2005) proposed an optimum design technique applied to determine optimum geometry for bridge decks and properties of the FRP material by carrying out three-dimensional numerical modelling. An experimental and analytical study regarding the comparison between different FRP bridge deck panels load-deflection behaviour under design truck wheel load and their evaluation according to Ohio Department of Transportation (ODOT) criteria was published by (Alagusundaramoorthy, 2006). (Lee, 2007) conducted flexural tests on a bridge deck system for light-weight vehicles made from square cellular profiles, to characterize its flexural behaviour under static loading conditions. Both laboratory and field tests were used by (Jeong, 2007) to evaluate the performance of a GFRP deck consisting of double-rectangular cells profiles under truck loads. The static behaviour of an orthotropic bridge deck made of glass fibre reinforced polymer (GFRP) and polyurethane foam was investigated experimentally by (Zi G, 2008) where a new type of cross section was proposed. A larger scale structure made from a similar deck system and a steel superstructure was tested by (Majumdar, 2009) for evaluating its performance under different service load conditions. (Vyas, 2009) experimentally evaluated, according to AASHTO requirements, a deck system for moveable bridges composed of mechanically fastened pultruded FRP parts. Tests were performed on two-span deck specimens, both perpendicular and with 30º skew to the supporting girders. Finally, (Sebastian WM., 2012) presented results from 3D finite element analyses (FEA) of loaded isolated and bridge specimens, which captured the complex influences of local and global indeterminacies on the response of FRP decks in deck-on-beam bridges.

2.

Present Study

This report presents a combined experimental and analytical study of FRP cellular deck specimens under wheel load. Test campaign was carried out on an instrumented specimen of a portion of bridge deck system with 1,40 m of length, in which static concentrated loads were transmitted to the specimen via square-in-plan steel plate faced with elastomeric pad. The experimental data of a singlespan specimens previously tested at IETcc in 2012 are used to compare the results from numerical models. In addition, an effort was made to study the effect of aging of the material on the structural response. On the other hand, numerical models of isolated specimen and bridge specimens were analyzed using the finite element method. The test data were compared to the numerical results, FEA, which was used to model the above-described complex stiffness profiles. The FEA is then used to predict the relative significances of the global and complex local effects in the longitudinal and transverse directions of the bridge. Specimen used in this study employed the FRP cellular deck of section shown in Figure 2. The 200 mm side length of the square plate was taken from published work by (Daly AF, 2006). The dimension of the specimen – shown in Figure 4 – is 1,40 m x 0,20 m x 0,22 m (length x width x height), rigidly supported portion bridge deck. Therefore, the experimental data obtained from this specimen represent the effects of local responses to the applied concentrated loads. Such data were obtained for several locations of the loads showing particularly high strains at the local joint and midspan zones of the section. Specimens tested in 2012 – shown in Figure 7 – are 3,30 m of length, 1,40 m of width, single span simply supported bridge comprising the FRP deck. Hence, the experimental data obtained from this specimen represent the combined effects of global and local responses to the applied concentrated loads.

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2.1. Outline of research project In our study, we were interested in the behavior of the pultruded GFRP deck considering the use of new and replacement bridge decks. The report includes a description of the FRP deck, the numerical simulation, the testing and a summary of the performance of the deck. In each of the following sections, the discussions for the isolated specimen – focused on local effects – are presented firstly, after which the bridge specimen – global effects – are given. The report is arranged as follows: Section 1 gives an introduction of the glass FRP material, its use in bridges and a background of experimental studies. Initial considerations of the research are exposed in Section 2. The finite element model is given in Section 3. The specimen preparation and experimentation are showing in Section 4. We discuss the experimental results in Section 5. Finally, we draw conclusions of this study in Section 6.

2.2. Deck System The evaluated GFRP deck system for traffic bridges is assembled from single modular profiles with a double-rectangular cell. The profile was formed through a pultrusion process. Geometry and dimensions in mm of the unit module are shown in Figure 2. Each profile is 400 mm x 220 mm (width x height) and weighs 28.90 kg/m. Unit profiles are then adhesively bonded along their outer webs using a structural bi-component epoxy adhesive.

Figure 2. GFRP profile shape.

2.3. Material Properties Constituent materials of the GFRP profiles consist of E-glass fibers (mainly unidirectional E-glass roving) and vinyl ester resin. Mechanical properties of the deck laminate components were obtained through coupon tests performed at IETcc in 2012, which are shown in Table 1. Strengths (S) and Young’s elastic modulus (E) are listed. The following subscripts are used: (1) for the laminate’s pultrusion direction equal to the deck’s longitudinal direction; (2) for the traffic direction or deck’s transverse direction, perpendicular to 1 direction; (t) for tension and (c) for compression. Longitudinal direction and transverse direction of the single-span deck are shown in Figure 3.

Figure 3. Pultrusion direction and traffic direction.

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Table 1. Components mechanical properties.

Component Top flange Bottom flange Web

Thickness [mm] 20 14 11

Longitudinal properties S1,c E1,t E1,c [MPa] [GPa] [GPa] 33,338 499 31,903 466 517 29,400 30,284

S1,t [MPa]

S2,t [MPa] 42 62

Transverse properties S2,c E2,t E2,c [MPa] [GPa] [GPa] 12,844 11,153 170 14,367

Source: Coupon tests performed at IETcc in 2012

2.4. Isolated specimen A portion of deck panels for testing was composed of four unit pultruded profiles adhesively bonded and had a transverse section consisting of eight rectangular cells. Panel was 1440 mm x 200 mm x 220 mm (length x width x height). Tests were conducted on specimens without road surface. Further, this specimen was rigidly supported at its base – shown in Figure 4 – so that only local effects developed in the deck under applied load.

Moveable load system

Figure 4. Elevation of the isolated specimen test setup.

Load was applied from a servo-hydraulic actuator onto the 200 mm x 200 mm square-in-plan steel plate faced with a 10 mm thick elastomeric pad resting on the top flange of the deck. The load was moved along the specimen in increments of 40 mm to permit inference of strain influence lines. Specimen were loaded up to a concentrated wheel load of 10 kN. Figure 5 shows the plate-pad directly over the cell – henceforth termed central cell – which was significantly strain gauged. This datum, with the pad centered at midspan of the upper flange, is henceforth termed the ‘‘zero’’ load location. The pad was moved up to -570 mm left side and +330 mm of this zero location. Henceforth, with respect to the zero location, movement to the right is taken as positive. The direction of incremental movement of the load represents the direction in which the traffic would flow for the deck-on-beam type of road bridge in practice.

Figure 5. Movement of plate-pad system along specimen.

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Figure 6 shows the comprehensive layout of strain gauges – including those on the internal flange and web surfaces, made possible by employing a narrow width of specimen – for this experiment. Each gauge was placed at the longitudinal centerline of the specimen and was oriented to measure strain along the length of the relevant web or flange. At each instrumented section a pair of electrical resistance gauges was used – one gauge on each surface of the relevant web or flange – to permit decoupling of local axial from local flexural effects.

Figure 6. Layout of strain gauges (black rectangles) on webs and flanges.

2.5. Bridge specimens A part of the IETcc project developed in 2012, several tests were carried on single-span specimens for different span lengths and truck wheel load locations. Each of them was composed of four unit pultruded profiles adhesively bonded and had a transverse section consisting of eight rectangular cells. Panels were 3300 mm x 1387 mm x 220 mm (length x width x height). Flexure static tests were carried out within that study to evaluate the GFRP deck panels performance for the Service Limit State (SLS) according the Eurocode loading conditions. Specimens were tested under three-point bending for two different span lengths (2000 mm and 2500 mm) and two different positions of the loading patch with regard to the GFRP deck panel transverse section (loading directly two or three webs) as shown in Figure 7. Specimens were loaded up to a concentrated wheel load of 150 kN.

Figure 7. Single-span bridge specimens. Source: Tests performed at IETcc in 2012

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As mentioned above, bending tests with the same load configuration were conducted for three specimens. An overview of which is provided in Table 2. Test appellation used within 2012 study was as follows: -

First two characters (S1, S2, S3) indicate the specimen number. The third character (S, L) refers to span length; S (short) was used for 2000 mm span and L (large) for 2500 mm span. The fourth character (2, 3) denote whether the load is applied affecting directly two or three panel webs, respectively. Table 2. Overview of the tests performed. Specimen

Appellation

S1, S2, S3

S-S2 S-S3 S-L2 S-L3

Span [mm] 2000 2000 2500 2500

Webs loaded two three two three

Applied load [kN] 150 150 150 150

Source: Tests completed at IETcc in 2012.

3.

Numerical Simulation

Finite element bridge deck models were developed by using the commercial FE software ABAQUS through an imported CAD model of each specimen. As an initial approximation, four different idealizations were modeled. The first three simplified models considered the structure (1) in a state of plane strain, (2) in a state of plane stress and (3) shell elements, and on the other case contemplated (4) like a 3-D complex structure. The differences in terms of displacements, strains and stresses in each element were very significant. The assumptions enclosed in continuum mechanics for this simplified models were not valid in our specimens due to particular deck geometry where the thickness of flanges and webs was thick enough to not take for good thickness restrictions in lamina theory, in addition, the conditions of plane strain and plane stress were not met. Reliable structural response and closer to reality were obtained with the 3-D model. Henceforth, the type of finite element used in the analysis is an eight node linear 3-D brick element with reduced integration (C3D8R). It is assumed that all parts of the deck system are perfectly bonded together. The discretization of the specimens is shown in Figure 8.

Figure 8. Finite element models of isolated and bridge specimens.

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One of the most demanding parameters during the FE modeling of the structure was the material modeling. In this analysis, GFRP is assumed like orthotropic material and the fiber directions are supposed to be unidirectional, so that each direction has its own elastic modulus (E). The results presented henceforth assume a Poisson’s ratio equals to 0,34. A unique value for shear modulus of 4,0 GPa was supposed according a recommendation of (Bank, 2006) for GFRP. There are three degrees-of-freedom (3D translations) per node for every element. A uniform distribution of load was assumed in the FE model over the patch mapped out at the top of the steel plate, to represent the contact with the wheel load. Finally, one load step per every single location was used. As regards the isolated deck specimen modeling, in order to obtain influence lines for strains to compare to the test data, a parametric FE study was conducted in which the profile load is moved to different locations incrementally along the transverse direction (X-axis) of the model in steps of 40 mm. Boundary conditions was pinned supports (no X, Y, Z translations for nodes along the base of the specimen). Figure 9 shows X-axis stress (xx) distribution for cellular deck under wheel load of 10 kN located above central cell.

Load

Central Cell

Figure 9. Stress - xx - distribution.

With reference to the bridge specimen modeling, maximum deflections and strains were obtained for two different positions of the loading patch (above two or three webs) and support distances. Boundary conditions of roller supports – free X and Z translations but no Y translations for nodes along two transverse lines at the base – near the ends of the structure were input to the model. The deflection contour of deck panel subjected to a middle-span load of 150 kN is shown in Figure 10.

Load

Figure 10. Deflection contour of GFRP deck panel.

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For both the isolated and the bridge specimens, FE-predicted nodal strains were taken from the elements closest to the strain gauge locations in the actual specimens. Some of the structural details are left out in the model and more focus is given on capturing the response of the GFRP deck itself. Therefore, adhesive joint is not modeled in the current analysis. A special software program was written in the software PYTHON to output the results and to plot strength–strain curves. Results of FEA simulation along with experimental observations are discussed in the following sections.

4.

Testing Campaign

4.1. Test Preparation This type of panels is intended to be installed with its longitudinal (pultrusion) direction perpendicular to traffic direction. They are supported by stringers parallel to traffic direction and spaced at a maximum distance of 2.50 m. Test set-ups did not take into account any deck panels support on girders and connections between them. Only the deck’s behavior was studied. Coordinate system used within this study can be seen in Figures 5 and 8. It is as follows: X-axis indicates traffic direction and is transverse to panel pultrusion direction; Z-axis indicates direction transverse to traffic direction and is parallel to panel pultrusion direction; and Y-axis indicates thickness of the deck and is also transverse panel pultrusion direction. A purpose-built test frame made of steel sections is being used to house and apply loads to the isolated specimen. In order to approximate a tire at top surface, a servo-hydraulic actuator – supported from the test frame – was used to apply loads to the deck by plate-pad system for each location as shown in Figure 11.

4.2. Loading plan Two tests were performed at the same specimen: service load test and failure test. For the first one, the loading pads were arranged along the deck’s transverse direction, labelled L1 to L18 where “L” means “Load”. The locations of loading patches were designed to simulate the “worst-case” scenarios on a real bridge under truck load. The mounted hydraulic jack had a capacity of 120 kN and was controlled using a load control unit – Figure 11. During test, the specimen was monotonically loaded at 2 kN/min rate and data were continuously recorded. On the other hand, for the failure test the L12 load position was chosen. The patch load was located at +82 mm (from the “zero” point) which location corresponds to the axis of the right web of central cell. In this case, the mounted hydraulic jack had a capacity of 500 kN and the specimen was monotonically loaded at 20 kN/min rate. Loads were distributed through square steel plate 200 x 200 x 25 mm3. Rubber pad 200 x 200 x 10 mm3 were placed between steel plate and deck specimen top surface to minimize the abrasion between them.

Figure 11. Test set-up.

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4.3. Instrumentation Specimen instrumentation consisted of electrical resistance strain gauges for strain measurements (TOKIO SOKKI 5.0 mm gauge length). Fourteen strain gauges were used in total (6 flange gauges and 8 web gauges) as shown in Figure 6. Strain gauges and load cell were connected to a data logger, which continuously recorded data during testing. Flange strain gauges, in X-direction, were placed both on top and bottom faces of the upper flange. Web strain gauges, in Y-direction, were placed both on outer and inner faces of the central cell’s webs. Both types mainly located along specimen central sections as shown in Figure 12. strain gauge

Figure 12. Isolated specimen instrumentation.

4.4. Service load test In order to verify the strength-strain curves of the GFRP deck’s numeric model proposed, the service load test was performed on the isolated specimen under wheel load configuration as shown in Figure 5. These rectangular loading patches of 200 mm x 200 mm were used to simulate the action of wheel loads of vehicle on the top of the deck. The design wheel load was 10 kN. The specimen was rigidly supported at its base using a steel beam extended 0.25 m beyond the specimen ends. The specimens satisfy the linear elastic behavior throughout the test. During the whole process of the loading history, neither visible nor audible damage occur in the deck specimen.

4.5. Failure Test For failure test of the GFRP deck, only one loading configuration was considered where the same tire patch is used with a +82 mm center-to-center distance of about “zero” point as shown in Figure 13. The deck is loaded until initiation of failure and measurements are recorded in situ. Failure is detected by large variations in strain data with increasing load. Also, there has been a huge audible sound indicative of failure. The cause of the sounds may involve in the multiple damage such as fiber breakage, matrix cracking, delamination, or a combination of these failures. The failure started at 300kN and occurred at the loaded web.

0

+82mm

Internal delamination Central Cell

Figure 13. Web’s bottom failure.

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Failure was observed to be localized at the bottom of the web under the loading patch. The failure is due to high strain – perpendicular to pultrusion direction – because the composite lay-up in the pultruded shape is predominantly unidirectional and the laminate is weak in transverse direction. Using finite-element model, failure analysis is carried out to investigate the failure status of each component in the cellular GFRP deck and verified against experimental observations. Transverse strain values are found to be significantly higher at the right web of the cellular structure than other sites. Again, failure is localized on the web under the loading patch and this is consistent with the experimental observations.

5.

FE – Test Comparisons

5.1. Local Behavior of Cellular Deck To explore the local response of the cellular FRP composite deck, a three-dimensional finite-element model and service load test were performed in the isolated specimen. All results presented bellow were obtained for a peak applied load of 10 kN. As a relevant consideration, the tensile strains are positive. From the strains response, it is clear that the deformation behavior is mainly localized under the loading area and enclose the top flange of the cell and two nearby webs. In addition, stress and strain distribution patterns – from FEA – in the instrumented zones within and near central cell of Figure 6 also demonstrate similar localized response as shown representatively in Figure 14, for the local midspan of upper flange, and in Figure 15, for the right web of central cell. The load position on each horizontal axis is considered respect to the location “zero”, defined earlier.

Figure 14. Isolated specimen: FE strain and stress influence lines for upper flange (10 kN load).

Figure 15. Isolated specimen: FE strain and stress influence lines for right web (10 kN load).

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A sketch of the specimen deck is presented on the right side of Figure 14 and 15 to identify the strain gauge locations. Then, on the actual plot of Figure 14, terms 4a and 4b allow the identification of the gauge locations. In Figure 15, it is shown that these two gauges – 8a and 8b – are located at the right hand thick web. For each load location on each plot, ‘‘a’’ strain minus ‘‘b’’ strain relates to local flexing at the flange or web section concerned, while the average of the two strains (yellow dash line) relates to the local axial force carried by the section. Note that all strains were observed to vary linearly with load. From the FE data in Figures 14 and 15, the following statements may be deduced: -

Symmetric behavior of the gauge pair plots (4a, 4b) related to the travelling load locations is observed due to the model assumed perfect alignment of the deck units in the bridge specimen.

-

Significant tensile strain ranges (up to 300  for both the flanges and the webs) occurred as the load position is changed. The higher strain value is obtained for the load pad over midspan of the central cell, at zero point.

-

Intersection of the ‘‘a’’ and ‘‘b’’ strain plots on each graph indicates reversal of local curvature in the plate with load movement. Reversal is sharp for the web at the joint, but not for the flange either at the joints or at mid-span.

-

For the web, the average strain (yellow dash line) is largely (though not always) negative, which means that the axial force is largely compressive as the load moves across. The peak axial force occurs when the pad is over the middle of the joint adjacent to the web. This matches with the role of the webs in transmitting the pad loading to the rigid support of the specimen.

From the failure test of the GFRP deck, valuable information about aging and degradation of GFRP could be inferred. First of all, the isolated specimen remained in weathering conditions (solar radiation, wind, rain, pollution, etc.) at IETcc playgrounds for 3 years. Only the first third range of the loading procedure was considered from the failure test data, namely until a peak load of 100 kN where the loaded web behavior is linear elastic. This data helped to deduct the mechanical properties (stiffness) degradation of the bridge deck system. Despite the lack of test data about durability studies in this type material, degradation mechanisms and the effects of environment parameters such as moisture, salt solutions, alkaline on the durability of FRPs were presented and discussed as part of the International Workshop “Aging of Composites“ (Benmokrane, 2013). On a similar way, (Wang Y., 2009) performed a durability study with accelerated ageing test of glass-fiber reinforcement polyester composites (GFRPC), in which concluded that the main influencing factor leading to the failure of this material is UV irradiation.

Figure 16. Stiffness aging – Young’s modulus for loaded web.

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Analyzing the test data, 80% of the load is carried by the central web and 20% by the two nearby webs. Because of the effects of weathering, there are disparities in the slopes of the load-strain curves between FE and test results. Analytical calculations of the webs response were fulfilled to determine the percentage of reduction on the Young`s modulus to replicate the experimental strains. Thus, a decision was made to develop a new FE model which stiffness experiences a degradation of 15%. The load–strain curves are generated in Figure 16, and ABAQUS results (lines) agree well with the experimental values (dots).

5.2. Global Behavior of Cellular Deck As regards the bridge specimens tests in 2012, the observed response of the load/deflection single span tests was linear elastic throughout the tests up to the applied service load. No cracks were heard neither observed during the tests, too. Deflection results of both the performed service load tests and FE-model are summarized in Table 3. This values correspond to deflection at midspan δ1/2 and quarter span δ1/4 on different specimens (S1, S2, S3). Obviously, maximum deflection is found for larger span length (L3) for the middle point (δ1/2). For a given specimen, a slightly less stiff behavior was noticed when the load patch was applied affecting only two panel webs instead of three. No significant differences in displacement test results (ranging from 5% to 10% at midspan) were detected within the same test type for different specimens, so the results seemed to be consistent. On the other hand, a disparity of 20% – on average – is observed between FE and test results, the theoretical values always higher. Table 3. Summary of FE and test results for SLS concentrated load of 150 kN. Test Theoretical* S1-S2 S2-S2 S3-S2 Theoretical* S1-S3 S2-S3 S3-S3 Theoretical* S1-L2 S2-L2 S3-L2 Theoretical* S1-L3 S2-L3 S3-L3

Span [mm]

Webs -

2000

two

2000

three

2500

two

2500

three

δ1/2 [mm] 6,04 4,71 4,75 4,93 5,57 4,62 4,61 4,80 9,15 6,89 6,62 7,07 8,50 6,58 6,19 6,69

δ1/4 [mm] 3,78 2,90 3,11 3,42 3,00 3,16 5,66 4,42 4,51 5,20 4,39 4,40

Max εzz+ Bottom [με] 923 908 1086 1057 866 846 1091 1079 1106 1030 1273 1230 1281 985 1226 1190

Max εxxTop [με] -106 -478 -619 -527 -197 -385 -544 -461 -157 -584 -706 -658 -292 -498 -650 -572

Source: Tests completed at IETcc in 2012. Note*: Present study FE response.

Load-longitudinal strain behavior was also linear elastic. Significant measured experimental values are also summarized in Table 3. In 2012 single-span tests was observed that the maximum positive longitudinal strain was measured in the bottom face, under the load application point. Strain gauge located under the central web recorded higher maximum strain values than gauge located in the bottom flange between two webs. The maximum negative longitudinal strain was measured in the top face, in the central longitudinal line and near the loading patch when it directly affected three panel webs. Gauge located above the central web and longitudinally aligned with the load, showed higher values than gauge located in the top flange between two webs. When the load was applied affecting only two webs, maximum negative longitudinal strain in specimens S2 and S3 was recorded also in the top face, but at midspan and near the loading plate. For bending moment, both in the bottom and in the top faces longitudinal strain is considerably higher in the center profiles than in the outer profiles. A disparity of 10% – on average – is observed between FE and test results for maximum positive strains (pultrusion direction), on the contrary for maximum negative strains the difference is extremely high.

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6.

Conclusions

From the work presented in this document, the following conclusions may be drawn, namely: -

FEA is a useful tool for capturing the complex influences of local and global indeterminacies on the response, to concentrated loads, of FRP decks. The complex stiffness distribution due to FRP anisotropies and to the plate-pad loading system are all reliably represented in the FEA.

-

The influence lines for the local strains are short, with concentrated load applied to the deck’s top flange within one FRP cell generating little local structural action in the continuous flange within the immediately adjacent cell.

-

Local deformation analysis of the cellular FRP composite deck provided vital information about variation of structural response - stress, strain - within the modular geometry. Stress at the top flange of the cellular structure can be much higher compared to the bottom span.

-

The verified FE analysis may be used to assist the FRP designers, allowing them to design suitable FRP bridge decks that meet the requirements for each specific project.

-

From strain experimental data, it is observed that the response of the deck is linear elastic under service load conditions with no evidence of damage initiation.

-

Careful attention is needed to prevent local damage in highly stressed regions of the supporting deck, such as web to flange connections and close to bearing supports.

Acknowledgements I would like to express my gratitude to IETcc and Carolina Foundation for providing the funds to this internship in Spain, and to IETcc personnel involved in the development of this work. Special thanks are due to the tutors for the technical and financial support, who enriched the research with their experience and advice.

References Alagusundaramoorthy, P. H. (2006). Structural Behavior of FRP Composite Bridge Deck Panels. Journal of Bridge Engineering. Bank, L. (2006). Composites for Construction, Structural Design with FRP Materials. Benmokrane, B. (2013). Durablility Issues of FRP for Civil Infrastructure. Proceedings of the International Workshop on Aging of FRP Composites. Ashburn, VA, USA: U.S. Department of Transportation. Daly AF, C. J. (2006). Performance of a fibre-reinforced polymer bridge deck under dynamic wheel loading. Composites Part A . Jeong, J. L. (2007). Experimental characterization of a pultruded GFRP bridge deck for light-weight vehicles. Composite Structures. Lee, J. Y. (2007). Experimental characterization of a pultruded GFRP bridge deck for light-weight vehicles. Composite Structures. Majumdar, P. L. (2009). Performance Evaluation of FRP Composite Deck Considering for Local Deformation Effects. Journal of Composites for Construction. Park K., K. S. (2005). Pilot test on a developed GFRP bridge deck. Composite Structures. Sebastian WM., R. J. (2012). Load response due to local and global indeterminacies of FRP-deck bridges. Composites. SIMULIA, Abaqus Analysis User's Manual, v6.13, Dassalt Systemes SIMULIA Corp., 2013. Vyas, J. Z. (2009). Characterization of a Low-Profile Fiber-Reinforced Polymer Deck System for Moveable Bridges. Journal of Bridge Engineering. Wang Y., M. J. (2009). Accelerated Ageing Tests for Evaluations of a Durability Performance of Glassfiber Reinforcement Polyester Composites. Journal of Materials Science Technology. Zhou, A. C. (2005). Laboratory and Field Performance of Cellular Fiber-Reinforced Polymer Composite Bridge Deck Systems. Journal of Composites for Construction. Zi G, K. B. (2008). An experimental study on static behavior of a GFRP bridge deck filled with a polyurethane foam. Composite Structures.

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